A garment, similar to the Oriental pyjama (which see), adopted among Europeans, Americans, and other Occidentals, for wear in the dressing room and during sleep; also, a suit of drawers and blouse for such wear. [Webster 1913 Suppl.]
pyjamas, n.pl. (US pajamas)
1 a suit of loose trousers and jacket for sleeping in.
2 loose trousers tied round the waist, worn by both sexes in some Asian countries.
3 (pyjama) (attrib.) designating parts of a suit of pyjamas (pyjama jacket; pyjama trousers).
Etymology
Urdu pa(e)jama f. Pers. pae, pay leg + Hindi jama clothing